pkcon install fails -- proxy?

[tlc]

Xenial Desktop. I am behind a proxy but have no idea how to configure a proxy for pkcon.
Proxies are set and working in /etc/environment and /etc/apt

 $ sudo apt-get install packagekit-tools

 $ pkcon install pianobar
Command failed: The proxy could not be set: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/dbus/service.py", line 654, in _message_cb
    (candidate_method, parent_method) = _method_lookup(self, method_name, interface_name)
  File "/usr/lib/python3/dist-packages/dbus/service.py", line 246, in _method_lookup
    raise UnknownMethodException('%s is not a valid method of interface %s' % (method_name, dbus_interface))
dbus.exceptions.UnknownMethodException: org.freedesktop.DBus.Error.UnknownMethod: Unknown method: SetProxy is not a valid method of interface org.freedesktop.PackageKit

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: packagekit-tools 0.8.17-4ubuntu6~gcc5.4ubuntu1.2
ProcVersionSignature: Ubuntu 4.4.0-124.148-generic 4.4.117
Uname: Linux 4.4.0-124-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CurrentDesktop: Unity
Date: Thu May 31 15:39:40 2018
InstallationDate: Installed on 2015-01-08 (1239 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: packagekit
UpgradeStatus: Upgraded to xenial on 2016-09-23 (615 days ago)

[Matthias Klumpp (ximion)]

This very much looks like a bug int Aptdaemon's PK compatibility layer to me. At this point, it likely makes no sense to fix this issue, since that code has been dropped after the Xenial release.

@tlc: This will likely be a won't fix bug, please upgrade to Bionic if you can. If you can't upgrade, you can try to switch from the compat layer to the real PK daemon, if the system allows you to do that:
sudo apt purge python3-aptdaemon.pkcompat ; sudo apt install packagekit

[tlc (tlc)]

Any idea of the implications of doing this?

> sudo apt purge python3-aptdaemon.pkcompat ; sudo apt install packagekit

There must be a reason Xenial had that, despite packagekit existing.